
/**
 * js中布尔值为false的六种情况  https://www.cnblogs.com/zjx304/p/9782942.html
 * 假：false、数字零(+0, -0, 0.0)、 NaN, 空字符串、undefined, null
 * 真：其他所有情况
 *
 * @type {[type]}
 */
var a, b = null ;
var a1 = '', b1 = 0, c1 = false ;
var a2 = NaN ;

// console.log(undefined == a, undefined == b);
// console.log(undefined == a1, undefined == b1, undefined == c1);
// console.log(undefined == a2);


// console.log('-----------------------\n')

// console.log(null == a, null == b);
// console.log(null == a1, null == b1, null == c1);
// console.log(null == a2);



// null -> number  0 
// undefiend -> number  NaN
// 将null, undefiend 都转为number为0 的方法 val >>> 0
// console.log(+b, Number(b), b >>> 0);
// console.log(+a, Number(a), a >>> 0);








